Creating a Volume for Use as a Full-Sized Instant Snapshot
If you want to create a full-sized instant snapshot for an original volume that does not contain any spare plexes, you can use an empty volume with the required degree of redundancy, and with the same size and same region size as the original volume.
To create an empty volume for use by a full-sized instant snapshot:
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Use the vxprint command on the original volume to find the required size for the snapshot volume.
# LEN='vxprint [-g diskgroup] -F%len volume'
Note
The command shown in this and subsequent steps assumes that you are using a Bourne-type shell such as sh, ksh or bash. You may need to modify the command for other shells such as csh or tcsh.
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Use the vxprint command on the original volume to discover the name of its DCO:
# DCONAME='vxprint [-g diskgroup] -F%dco_name volume'
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Use the vxprint command on the DCO to discover its region size (in blocks):
# RSZ='vxprint [-g diskgroup] -F%regionsz $DCONAME'
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Use the vxassist command to create a volume, snapvol, of the required size and redundancy, together with a version 20 DCO volume with the correct region size:
# vxassist [-g diskgroup] make snapvol $LEN \
[layout=mirror nmirror=number] logtype=dco drl=off \
dcoversion=20 [ndcomirror=number] regionsz=$RSZ init=active \
[storage_attributes]
Specify the same number of DCO mirrors (ndcomirror) as the number of mirrors in the volume (nmirror). The init=active attribute is used to make the volume available immediately. You can use storage attributes to specify which disks should be used for the volume.
As an alternative to creating the snapshot volume and its DCO volume in a single step, you can first create the volume, and then prepare it for instant snapshot operations as shown here:
# vxassist [-g diskgroup] make snapvol $LEN \
[layout=mirror nmirror=number] init=active [storage_attributes]
# vxsnap [-g diskgroup] prepare snapvol [ndcomirs=number] \
regionsize=$RSZ [storage_attributes]
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